1. Field of the Invention
The present invention relates to an input/output card of a PC card conforming to the PCMCIA standard, and relates particularly to a multiple function PC card comprising two or more functions of which none are used simultaneously.
2. Description of the Prior Art
FIGS. 5A and 5B are block diagrams of a conventional PC cards conforming to the PCMCIA standard, FIG. 5A showing a conventional modem card, and FIG. 5B showing a conventional communications card used with a portable telephone.
Referring to FIG. 5A, a modem card 51 comprises a PC interface connector 52 conforming to the PCMCIA standard for connecting the modem card 51 to a personal computer or other computing device; an interface IC 53 conforming to the PCMCIA standard; circuitry 54 executing the various functions of the modem card; an input/output (I/O) circuit block 55 providing the interface between the circuitry 54 and the external device connected to the modem card 51; and a device connector 56 for connecting an external device to the modem card 51, and provided on the modem card 51 at a position relative to the PC interface connector 52. One connector 57 of the connector cable 58 connecting the modem card 51 with the external device is connected to the device connector 56, and the other cable connector, which is typically a modular jack, is connected to the external device, typically the telephone network interface (line) connector for a modem card 51 such as this.
The communications card 61 shown in FIG. 5B similarly comprises a PC interface connector 62 conforming to the PCMCIA standard for connecting the communications card 61 to a personal computer or other computing device; an interface IC 63 conforming to the PCMCIA standard; circuitry 64 executing the various functions of the communications card; an input/output (I/O) circuit block 65 providing the interface between the circuitry 64 and the external device connected to the communications card 61; and a device connector 66 for connecting an external device to the communications card 61, and provided on the communications card 61 at a position relative to the PC interface connector 62. One connector 67 of the connector cable 68 connecting the modem card 61 with the external device is connected to the device connector 66, and the other cable connector is connected to the external device, a portable telephone in this example.
Single PC card such as these thus typically provides only a single function. As the degree of integration achievable in integrated circuits has risen, however, both the number and size of the components required to achieve a single function have decreased, creating empty space in the PC card and making it possible to incorporate two different functions in a single PC card. This has led to the development of multiple function PC cards combining two different functions, e.g., LAN card and modem card functions or modem card and SCSI card functions, in a single PC card. By thus providing plural functions and capabilities in a single PC card, the unit cost per function is decreased. In addition, personal computers and personal digital assistants (PDA) commonly have only one or two PC card slots, and combining plural functions in a single card eliminates the need to carry plural cards to achieve the same functionality.
Conventional multiple function PC cards combining the functions of two or more single function cards are designed assuming the simultaneous use of two functions, and provide discrete device connectors for each function on the PC card. Because it is also possible to switch immediately between functions, the control circuitry is complex, making it difficult to further reduce cost. Combining the functions of a modem card and a communications card as described above into a single PC card is extremely efficient and convenient when accessing a data network from a remote location (e.g., when away from one's office). On the other hand, because these two functions cannot be used simultaneously over a single telephone connection, the complex circuitry enabling simultaneous use of two functions in conventional multiple function PC cards is extremely wasteful, resulting in a cost that is higher than necessary.